The performance of bipolar transistors is strongly affected by temperature variations. These variations in temperature manifest themselves as a shift in the junction potential of the device. As temperature decreases, junction potential increases rather dramatically.
Compensation schemes of the prior art, implemented externally to the device itself, simply increase or decrease input drive level to track the varying junction potential. This compensation method places increased demand on the stage being used to drive the bipolar transistor under consideration, and adds cost and complexity to external circuitry. Also, at extremely low temperatures, it is possible that the device may never turn on due to depletion of intrinsic carriers in the base region.
Accordingly, a need arises for a method for compensating a bipolar transistor for variations in junction potential caused by changes in temperature. The method should adequately compensate for decreases in intrinsic carrier concentration, but should not add undue complexity or cost to eventual circuit designs.